Chemistry and Biochemistry of HCA.pdf - AFBoard.com

10 J. Agric. Food Chem. 2002, 50, 10−22 

REVIEWS 

Chemistry and Biochemistry of (−)-Hydroxycitric Acid from 

Garcinia 

B. S. JENA, G.K.JAYAPRAKASHA, R.P.SINGH, AND K. K. SAKARIAH* 

Human Resource Development, Central Food Technological Research Institute, Mysore 570 013, India 

(-)-Hydroxycitric acid [(-)-HCA] is the principal acid of fruit rinds of Garcinia cambogia, Garcinia 

indica, and Garcinia atroviridis. (-)-HCA was shown to be a potent inhibitor of ATP citrate lyase (EC 

4.1.3.8), which catalyzes the extramitochondrial cleavage of citrate to oxaloacetate and acetyl-CoA: 

citrate + ATP + CoA f acetyl-CoA + ADP + P i + oxaloacetate. The inhibition of this reaction limits 

the availability of acetyl-CoA units required for fatty acid synthesis and lipogenesis during a lipogenic 

diet, that is, a diet high in carbohydrates. Extensive animal studies indicated that (-)-HCA suppresses 

the fatty acid synthesis, lipogenesis, food intake, and induced weight loss. In vitro studies revealed 

the inhibitions of fatty acid synthesis and lipogenesis from various precursors. However, a few clinical 

studies have shown controversial findings. This review explores the literature on a number of topics: 

the source of (-)-HCA; the discovery of (-)-HCA; the isolation, stereochemistry, properties, methods 

of estimation, and derivatives of (-)-HCA; and its biochemistry, which includes inhibition of the citrate 

cleavage enzyme, effects on fatty acid synthesis and lipogenesis, effects on ketogenesis, other 

biological effects, possible modes of action on the reduction of food intake, promotion of glycogenesis, 

gluconeogenesis, and lipid oxidation, (-)-HCA as weight-controlling agent, and some possible 

concerns about (-)-HCA, which provides a coherent presentation of scattered literature on (-)-HCA 

and its plausible mechanism of action and is provocative of further research. 

Keywords: Garcinia cambogia; Garcinia indica; Garcinia atroviridis; (-)-hydroxycitric acid; ATP:citrate 

lyase; fatty acid synthesis; lipogenesis; appetite; antiobesity 

INTRODUCTION 

Garcinia (family: Guttiferae) is a large genus of polygamous 

trees or shrubs, distributed in tropical Asia, Africa, and 

Polynesia. It consists of 180 species, of which ∼30 species are 

found in India (1). For the past several years, small and complex 

molecules have been isolated from the various species of 

Garcinia, which include xanthones and xanthone derivatives 

(2-4). However, the isolation of (-)-hydroxycitric acid [(-)- 

HCA] from a few species of Garcinia and its biological 

properties have attracted the attention of biochemists and health 

practitioners. 

The physiological and biochemical effects of (-)-HCA have 

been studied extensively for its unique regulatory effect on fatty 

acid synthesis, lipogenesis, appetite, and weight loss. The 

derivatives of (-)-HCA have been incorporated into a wide 

range of pharmaceutical preparations in combination with other 

ingredients for the claimed purpose of enhancing weight loss, 

cardioprotection, correcting conditions of lipid abnormalities, 

and endurance in exercise (5-22). 

In the present review attempts have been made to pool, 

analyze, and summarize the available information on the 

chemical, physiological, and biochemical aspects of (-)-HCA. 

SOURCES OF (-)-HCA 

(-)-HCA is found in the fruit rinds of certain species of 

Garcinia, which include G. cambogia, G. indica, and G. 

atroViridis (23-25). These species thrive prolifically on the 

Indian subcontinent and in western Sri Lanka (1, 26). 

G. cambogia is a small or medium-sized tree with a rounded 

crown and horizontal or drooping branches; its leaves are dark 

green and shiny, elliptic obovate, 2-5 in. long and 1-3 in. 

broad; its fruits are ovoid, 2 in. in diameter, yellow or red when 

ripe with six to eight grooves, and the fruits have six to eight 

seeds surrounded by a succulent aril. The tree is found 

commonly in the evergreen forests of Western Ghats, from 

Konkan southward to Travancore, and in the Shola forests of 

Nilgiris up to an altitude of 6000 ft. It flowers during the hot 

season, and fruits ripen during the rainy season. The seeds of 

G. cambogia contain 31% edible fat. 

10.1021/jf010753k CCC: $22.00 © 2002 American Chemical Society 

Published on Web 11/29/2001

Reviews J. Agric. Food Chem., Vol. 50, No. 1, 2002 11 

G. indica is a slender evergreen tree with drooping branches; 

its leaves are ovate or oblong lanceolate, 2.5-3.5 in. long and 

1-1.5 in. broad, dark green above and pale beneath; its fruits 

are globose or spherical, 1-1.5 in. diameter, dark purple when 

ripe and enclosing five to eight large seeds. The tree is found 

in the tropical rain forests of Western Ghats, from Konkan 

southward to Mysore, Coorg, and Wynaad. It flowers in 

November-February, and fruits ripen in April-May. The root 

is astringent. The seeds of the fruit have edible fat, commercially 

known as Kokam butter 

G. atroViridis is a moderate-sized graceful tree, 30-50 ft high, 

found in the northeastern districts of upper Assam. Leaves are 

6-9 in. long and 2-3 in. broad, thickly coriaceous, glabrous, 

abruptly acuminate, and base contracted; its flowers are terminal, 

the female flower being solitary and large. The fruits are orange 

yellow, subglobose (3-4 in. across), fluted with a firmly 

textured outer rind and a rather thin and translucent pulp 

surrounding the seeds (1). 

The fruits of G. cambogia are too acidic to be eaten raw. A 

decoction of the fruit rind is given for rheumatism and bowel 

complaints. It is also employed in veterinary medicine as a rinse 

for the diseases of the mouth in cattle. However, the fruit of G. 

indica has an agreeable flavor and a sweetish acid taste. It is 

used as a garnish to give an acid flavor to curries and also for 

preparing syrups during hot months. The fruit is also anthelmintic 

and useful in piles, dysentery, tumor, pains, and heart 

complaints. Syrup from the fruit juice is given in bilious 

affections. The fruits of both species are valued for their dried 

rinds, which are used as a condiment for flavoring curries in 

place of tamarind or lemon. In Ceylon the dried fruit rinds of 

G. cambogia are used along with salt in the curing of fish (1). 

The fruit rinds of G. atroViridis are also too acidic to be eaten 

raw, but the taste is excellent when stewed with sugar. In Malay, 

the sun-dried rinds of under-ripe fruits are sold as a sour relish 

for use in curries in place of tamarind and for the dressing of 

fish. The fruit is also used as a fixative with alum in the dyeing 

of silk. A decoction from leaves and roots is used in the 

treatment of earache (1). 

CHEMISTRY OF (-)-HCA 

Discovery of ())-HCA. The dried rind of the fruit of G. 

cambogia popularly known as “Malabar tamarind” is extensively 

used all over the west coast of South India for culinary purposes 

and commercially for “Colombo curing” of fish (23, 27, 28). 

The organic acids present in the fruit have been held responsible 

for the bacteriostatic effect of the pickling medium by lowering 

the pH (27). The fruit contains ∼30% acid calculated as citric 

acid on a dry weight basis (28). The organic acids present have 

been mistakenly identified as tartaric acid and citric acids (27, 

29). The aqueous extracts of the fruit showed two predominant 

acid spots on paper chromatograms run on different solvents, 

which were very near to tartaric and citric acids, but there was 

always a significant small difference in the R f values in all 

solvent systems. Analysis of the fruit juice by use of an ion 

exchange column as described by Palmer (30) showed the largest 

peak to be the citric acid region, but the acids failed the cream 

of tartar test for tartaric acid and the pentabromoacetone test 

for citric acid (28). 

Lewis and Neelakantan (23) isolated the principal acid in the 

fruit rinds of G. cambogia and identified it as (-)-HCA on the 

basis of chemical and spectroscopic studies. Identification and 

separation of the hydroxycitric acid on Whatman No. 1 paper 

were performed using n-butanol/acetic acid/water (4:1:5) and 

n-propanol/formic acid/water (4:1:5). The spots were identified 

by spraying with 5% metavanadate. Upon saponification of the 

Figure 1. Structures of hydroxycitric acid isomers. 

Figure 2. Structures of hydroxycitric acid lactones. 

acid mixture with excess alkali and passing it through a column 

of ion exchange resin (Zeocarb 215), the eluate showed only 

one lower spot (R f ) 0.34) corresponding to the free (-)-HCA. 

On concentration the eluate gave only one upper spot (R f ) 

0.46) corresponding to the lactone. Fruit extracts showed two 

predominant acid spots on chromatograms with two different 

solvent systems. On titration of this material with alkali, using 

phenolphthalein, two different end-points were obtained, in the 

cold and after boiling, showing the characteristics of lactones. 

The two spots on chromatograms were identified as hydroxycitric 

acid and its lactone (Figures 1 and 2). It was thus clear 

that the two spots on the chromatograms are those of γ-hydroxy 

acid and its lactone and not those of tartaric acid and citric acids. 

Isolation. Lewis and Neelakantan (23) isolated this (-)-HCA 

on a large scale from the dried rinds of G. cambogia. The 

method consisted of extracting the acid by cooking the raw 

material with water under pressure (10 lb/in. 2 for 15 min). The 

extract was concentrated, and pectin was removed by alcohol 

precipitation. The clear filtrate was neutralized with alkali, 

passed through cation exchange resin for recovery of the acid, 

which was concentrated and dried. The crude dried mass was 

extracted with ether and recrystallized to give small needleshaped 

crystals of lactone. Lewis (24) reported another method 

for the isolation of (-)-HCA from G. cambogia using acetone. 

The acetone extract was concentrated and the acid taken up in 

water. The aqueous solution yielded the lactone on evaporation. 

Moffett et al. (31) have developed a process for the aqueous 

extraction of (-)-HCA from Garcinia rinds. The extract was 

loaded onto an anion exchange column for adsorption of (-)- 

HCA, and it was eluted with sodium/potassium hydroxide for 

release of (-)-HCA. The extract was passed through a cation 

exchange column to yield a free acid. Guthrie and Kierstead 

(9, 10) and Moffett et al. (32) have reported the preparation of 

(-)-HCA concentrate from Garcinia rinds with 23-54% (-)- 

HCA and 6-20% lactone.

12 J. Agric. Food Chem., Vol. 50, No. 1, 2002 Reviews 

Table 1. Comparison of Physical Properties of HCA and Lactones 

from Garcinia and Hibiscus (23) 

property 

free 

acid 

Garcinia 

lactone 

free 

acid 

Hibiscus 

lactone 

mp (°C) 178 183 

[R] 20 D (deg) −20 100 122 31 

crystal shape needles needles 

hygroscopicity slight high 

solubility 

high in alcohol 

and water; fair 

in ether 

paper chromatogr (R f) 

butanol/formic acid/H 2O 0.24 0.42 0.15 0.39 

propanol/acetic acid/H 2O 0.26 0.36 0.35 0.26 

metavandate spray (5%) yellow reddish orange yellow yellow 

high in water 

and alcohol; 

slight in ether 

Stereochemistry. Hydroxycitric acid (1,2-dihydroxypropane- 

1,2,3-tricarboxylic acid) has two asymmetric centers; hence, two 

pairs of diastereoisomers or four different isomers are possible 

(Figure 1). Martius and Maue (33) have synthesized the four 

possible stereoisomers of hydroxycitrate. One of these isomers 

occurs in Garcinia (Figure 1, I) and another in Hibiscus species 

(Figure 1, II) (24). The absolute configurations of the hydroxycitric 

acid lactones, hibiscus acid and garcinia acid, were 

determined to be (2S,3R)- and (2S,3S)-2-hydroxycitric acid-2,5- 

lactone, respectively (Figure 2). The absolute configuration is 

determined from Hudson’s lactone rule, optical rotatory dispersion 

curves, circular dichrosim curves, and calculation of partial 

molar rotations (34). Glusker et al. (35, 36) have reported the 

structure and absolute configuration of the calcium hydroxycitrate 

and (-)-HCA lactone by X-ray crystallography. Stallings 

et al. (37) have reported the crystal structures of the ethylenediamine 

salts of diastereoisomeric hydroxycitrates. 

Properties of ())-HCA and Lactone. The physical properties 

of (-)-HCA and lactones (Figure 2) from Garcinia and 

Hibiscus are presented in Table 1. The equivalent weight of 

pure lactone is 69, as determined by alkali titration or silver 

salt decomposition. The IR spectra of the ethyl ester showed 

ester and hydroxyl groups at 5.41-5.76 and 2.74-2.79 µ, 

respectively (23). The structure of the (-)-HCA lactone was 

further established by IR and 1 H NMR spectroscopy. The (-)- 

HCA lactone displayed strong IR bands at 3200, 1760, and 1680 

cm -1 . 1 H NMR spectra of the (-)-HCA lactone showed two 

protons at the γ-carbon, which give an AB quartet at δ 2.53 

and δ 2.74 with J ) 17.1 Hz, and one proton at the R-carbon 

showing a singlet at δ 5.15 (38). 

Estimation of ())-HCA. Free (-)-HCA leads to the 

formation of (-)-HCA lactone during concentration and evaporation. 

The presence of minor organic acids such as citric acid, 

tartaric acid, and malic acid in the Garcinia fruits and the lack 

of official methods for the assay of (-)-HCA have created 

confusion and disagreement among analysts (39). The existing 

method for the determination of (-)-HCA content in G. 

cambogia extract involves acid-base titration, which gives the 

total acidity of the extract (40). However, in this method the 

concentrations of (-)-HCA and lactone cannot be estimated 

separately. 

Lowenstein and Brunengraber (25) have estimated the hydroxycitrate 

content of the fruit of G. cambogia by gas 

chromatography (GC). GC estimation involves the conversion 

of acid to volatile silyl derivative. They used an OV-17 GC 

column (3 m × 3 mm i.d.). The column was run at 145 °C 

using nitrogen as the carrier gas (40 mL/min) with an injection 

port temperature of 250 °C and a detector temperature of 300 

°C. (-)-HCA lactone is the major constituent of the extract, 

Figure 3. Structures of hydroxycitric acid derivatives. 

and the recrystallized compound contains


for the purified enzyme than the natural substrate, that is, citrate, 

and the K i of (-)-HCA for citrate cleavage enzyme was between 

0.2 and 0.6 µM depending on the conditions (47, 48). Later on, 

Cheema-Dhadli et al. (49) found inhibition of citrate cleavage 

enzyme by both free (-)-HCA (K i ) 8 µM) and (-)-HCA 

lactone (K i ) 50-100 µM). The lactone of (-)-HCA was found 

to be a very less effective inhibitor of citrate cleavage enzyme. 

In rat brain synaptosomes, (-)-HCA was shown to be a potent 

inhibitor of citrate cleavage enzyme (50). Sullivan et al. (51) 

and Stallings et al. (37), in similar studies, observed that of four 

isomers of HCA (Figure 1), (-)-HCA was the only potent 

inhibitor of ATP:citrate lyase. (-)-HCA was found to inhibit 

partially purified ATP:citrate lyase from human liver competitively 

with respect to citrate (K i ) 3 × 10 -4 M) (52). 

The discovery of the powerful inhibition of citrate cleavage 

enzyme by (-)-HCA provides a valuable tool for the study of 

the metabolic role of citrate cleavage reaction (47). 

The biological effect of (-)-HCA stems from the inhibition 

of extramitochondrial cleavage of citrate to oxaloacetate and 

acetyl-CoA. The ultimate source of all the carbon atoms of fatty 

acids is acetyl-CoA, formed in the mitochondria by the oxidative 

decarboxylation of pyruvate, the oxidative degradation of some 

of the amino acids, or the β-oxidation of long-chain fatty acids. 

The synthesis of fatty acids is maximal when carbohydrate is 

abundant and the level of fatty acids is low. The conversion of 

carbohydrate into fat involves the oxidation of pyruvate to 

acetyl-CoA. Fatty acids are synthesized in the cytosol, whereas 

acetyl-CoA is formed from pyruvate in mitochondria. For fatty 

acid biosynthesis, the acetyl group of acetyl-CoA must be 

transferred from the mitochondria to the cytosol. Acetyl-CoA 

as such cannot pass out of the mitochondria into the cytosol. 

The barrier to acetyl-CoA is bypassed by citrate, which carries 

acetyl groups across the inner mitochondrial membrane. Citrate 

is formed in the mitochondrial matrix by the condensation of 

acetyl-CoA with oxaloacetate. When present at high levels, 

citrate is transported to cytosol, via the tricarboxylate transport 

system. In cytosol, acetyl-CoA is regenerated from citrate by 

the ATP:citrate lyase, which catalyzes the following reaction: 

citrate + ATP + CoA f acetyl-CoA + ADP + P i + 

oxaloacetate (53-57). ATP:citrate lyase is widely distributed 

in animal tissues (58). ATP:citrate lyase has been suggested to 

play a physiological role in lipogenesis from carbohydrate (59) 

and gluconeogenesis (60). The changes in activity of citrate 

cleavage enzyme correlate with changes in the rate of fatty acid 

synthesis and provide evidence for the involvement of the citrate 

cleavage reaction in fatty acid synthesis (61, 62). The activity 

of citrate cleavage enzyme varies in accordance with the 

nutritional status of the animal. Thus, during starvation or when 

fed on a high-fat diet, the enzyme levels fall drastically and on 

feeding of a high-carbohydrate diet elevated levels of ATP: 

citrate lyase were detected (61, 63). Evidence also exists 

demonstrating that >80% of the extramitochondrial acetyl-CoA 

produced from pyruvate in rat liver mitochondria is supplied 

via ATP:citrate lyase (64). 

Effect of ())-HCA on Fatty Acid Synthesis and Lipogenesis. 

(-)-HCA being a potent inhibitor of ATP:citrate lyase, 

which catalyzes the extramitochondrial cleavage of citrate to 

oxaloacetate and acetyl-CoA, limits the availability of acetyl- 

CoA units required for fatty acid synthesis and lipogenesis 

(65-68). Many studies demonstrated both in vitro and in vivo 

that (-)-HCA suppresses the de novo fatty acid synthesis and 

lipogenesis. 

In a cell-free system, consisting of particle-free cytoplasm 

and mitochondria prepared from rat liver, (-)-HCA was shown 

to inhibit fatty acid synthesis from citrate and also from [ 14 C]- 

alanine by measuring the incorporation of 3 H 2 O and 14 C(53). 

Sullivan et al. (65) studied the effect of stereoisomers of 

hydroxycitrate (Figure 1) on the rate of lipogenesis in rat liver. 

They found that only (-)-HCA significantly decreased the 

conversion of [ 14 C]citrate into lipid in the liver high-speed 

supernatant and the conversion of [ 14 C]alanine into lipid in vivo. 

Beynen and Geelen (69) observed the inhibition of fatty acid 

synthesis from glucose by (-)-HCA in isolated hepatocytes, 

but it did not affect fatty acid synthesis from acetate; rather, 

(-)-HCA was shown to stimulate fatty acid synthesis from 

acetate (70). This effect was observed both in the isolated 

perfused rat liver and in the homogenates of this organ and was 

assumed to be due to an activation of acetyl-CoA carboxylase 

in analogy to other tricarboxylates (71, 72). Moreover, the 

findings of Hackenschmidt et al. (73) showed that (-)-HCA is 

a positive effector of acetyl-CoA carboxylase and similarity of 

(-)-HCA and citrate activation of enzyme activity was apparent 

in the time for maximal stimulation. It was concluded that (-)- 

HCA acts as an inhibitor of lipogenesis only if cytoplasmic 

acetyl-CoA is produced by citrate cleavage enzyme reaction, 

but it will activate fatty acid synthesis wherever an alternate 

source of acetyl-CoA, for example, acetate, is available. 

The increase in lipogenesis in brown adipose in response to 

glucose feeding was inhibited by (-)-HCA (74). In starved rats, 

(-)-HCA did not inhibit the basal rates of brown fat lipogenesis 

and glucose utilization in response to insulin. As basal rates of 

lipogenesis were not inhibited by (-)-HCA, it is suggested that 

acetate may be a lipogenic substrate for brown fat in starvation 

(75). Smith (76) reported that rabbit adipose tissue has a low 

capacity for de novo fatty acid synthesis from glucose but a 

high capacity for synthesis from pyruvate and acetate. Experiments 

with (-)-HCA have demonstrated that citrate cleavage 

enzyme is an obligatory enzyme in lipogenesis from pyruvate 

and that the lipogenic system of rabbit adipose tissue resembles 

that of a ruminant in that it is adapted to utilize acetate rather 

than glucose. 

(-)-HCA partially inhibited the incorporation of 3 H from 

3 H 2 O and 14 C from [U- 14 C]lactate into saponifiable fatty acid 

in the hepatocytes from fed rats, but incorporation of 14 C from 

[ 14 C]proline was completely inhibited. However, similar complete 

inhibition of incorporation of 14 C from [ 14 C]proline was 

observed in fed rats, glycogen-depleted hepatocytes, or hepatocytes 

from starved rats (77). In another observation, (-)-HCA 

depressed lipogenesis in hepatocytes from fed rats incubated 

with lactate plus pyruvate by ∼51% but had little effect on 

lipogenesis in glycogen-depleted hepatocytes similarly incubated. 

There was a parallel inhibition of incorporation of 14 C 

from [U- 14 C]lactate to fatty acids, and lipogenesis was measured 

with 3 H 2 O in each case. Thus, depletion of glycogen or 

conceivably the process of glycogen depletion causes a change 

in the rate-limiting step(s) for lipogenesis from lactate (78). 

(-)-Hydroxycitrate markedly reduced tritiated water incorporation 

into fatty acid by lung tissue slices (79). Starving rats 

for 72 h markedly reduced in vivo 3 H 2 O incorporation into 

pulmonary lipids. Intraperitoneal injection of (-)-HCA prior 

to 3 H 2 O administration also markedly reduced isotope incorporation 

into pulmonary lipid fractions of fed rats. It has been 

concluded that in vivo synthesis of fatty acids was affected by 

the nutritional state of the animal and citrate appears to be a 

significant source of cytoplasmic acetyl-CoA for the de novo 

pulmonary lipogenesis in the fed rats (80). Sheehan and Yeh 

(81) observed that (-)-HCA inhibited fatty acid synthesis in 

neonatal rat lung from glucose, pyruvate, and β-hydroxybutyrate


by 88, 70, and 60%, respectively, but had no effect on that from 

acetoacetate. Lipogenesis from β-hydroxybutyrate involves both 

the cytoplasmic and citrate pathways. Crabtree et al. (82) 

observed that the fluxes of butyrate to acetate and fatty acids 

in rat hepatocytes were inhibited to a similar extent by (-)- 

HCA with no significant effect on butyrate uptake. Because 

butyrate is activated only in the mitochondria of rat liver (83) 

and (-)-HCA did not significantly inhibit butyrate uptake, this 

parallel inhibition of the flux of butyrate to acetate and fatty 

acids strongly suggests that the production of acetate occurs in 

the cytoplasm. (-)-HCA could not be expected to inhibit the 

production of acetate via the mitochondrial hydrolase. Experiments 

with (-)-HCA indicate that the major route for conversion 

of leucine carbon to lipid in rat mammary gland acini is via 

citrate translocation from the mitochondria (84). Mathias et al. 

(85) reported that in hepatocytes isolated from female rats, mealfed 

a high-glucose diet, (-)-HCA depressed the incorporation 

of 3 H 2 O, [ 14 C]alanine, [2- 14 C]leucine into fatty acids and 

cholesterol. 

Hood et al. (86) have shown that (-)-HCA reduced the 

synthesis of fatty acids from lactate and glucose in bovine 

adipose tissue and rat adipose tissue, respectively, and suggested 

that the conversion of lactate to fatty acids probably occurs by 

way of citrate. In the (-)-HCA-treated rat liver cells, there was 

a decrease in the formation of phospholipds and triglycerides 

from lactate (87). Vicario and Medina (88) have also reported 

the inhibition of lipogenesis from lactate in rat brain by (-)- 

HCA, and the transfer of lactate carbons through the mitochondrial 

membrane is accompanied by the translocation of citrate. 

(-)-HCA inhibited lipogenesis in rat brain slices (89, 90) 

and in freshly isolated mouse preputial gland (91). (-)-HCA 

equivalently reduced the biosynthesis of triglycerides, phospholipids, 

cholesterol, diglycerides, cholesteryl esters, and free 

fatty acids in isolated liver cells from normal and hyperlipidemic 

rats (92). (-)-HCA decreased the rate of cholesterol production 

in hepatocytes from fed rats by interfering with the flow of 

substrate into the sterol biosynthetic pathway (93). Measurement 

of the weight of desmosterol produced during its biosynthesis 

in the presence of tritiated water and triparanol has permitted a 

direct determination of the relative flux of carbon and tritium 

(the H/C ratio) into sterol in hepatocytes. The H/C ratio, which 

increased with the time of incubation, was shown to decrease 

with (-)-HCA. The depression of biosynthesis of long-chain 

fatty acids, 3-β-hydroxysterol, and cholesterol by (-)-HCA was 

confirmed in a perfused rat liver system (70, 94, 95). The 

inhibition of fatty acid synthesis by (-)-HCA was associated 

with the decreased rate of choline incorporation into desaturated 

phosphatidylcholine in fetal rat lung (96). Berkhout et al. (97) 

tested (-)-HCA in Hep G2 cells for effects on cholesterol 

homeostasis. After 2.5 and 18 h of incubation with (-)-HCA 

at a concentration of g0.5 mM, incorporation of [1,5- 14 C]citrate 

into fatty acids and cholesterol was strongly inhibited, which 

may reflect an effective inhibition of ATP:citrate lyase. Preincubation 

with a higher concentration of (-)-HCA increased the 

cellular low-density lipoprotein (LDL) receptor activity as 

determined by the receptor-mediated association and degradation. 

Measurements of receptor-mediated binding versus LDL 

concentration suggested that this increase might be due to an 

increase in the number of LDL receptors. A simultaneous 

increase of the enzyme levels of 3-hydroxy-3-methylglutaryl- 

CoA (HMG) reductase was also observed in the same condition. 

These results suggest that the increase in HMG-CoA reductase 

and LDL receptor are initiated by the decreased flux of carbon 

units in cholesterol synthetic pathway, owing to inhibition of 

ATP citrate lyase. 

Hildebrandt et al. (98) studied the utilization and preferred 

metabolic pathway of ketone bodies for the synthesis of lipids 

by freshly isolated Morris Hepatoma 777 cells, which are known 

to actively convert ketone bodies to cholesterol and fatty acid. 

On the basis of the results with (-)-HCA, these authors found 

that the metabolic pathway for acetoacetate conversion to lipids 

is exclusively cytoplasmic, whereas that for 3-hydroxybutyrate 

involves both extra- and intramitochondrial compartments. 

Acetyl-L-carnitine is known as a modulator of metabolic 

function. Lligona-Trulla et al. (99) have studied lipogenesis in 

different cell lines and in rat hepatocytes and observed that the 

flux of acetyl-L-carnitine (ALC) to lipid was increased, not 

decreased, by (-)-HCA. In contrast, this inhibitor dramatically 

decreased the flux of glucose to lipid. These results indicate 

that the flux of acetyl-L-carnitine to lipid can bypass citrate and 

utilize cytosolic acetyl-CoA synthesis, and it was shown that 

when (-)-HCA was used, the capacity of ALC to supply acetyl 

units for de novo lipogenesis could be increased significantly. 

Because ALC provides acetyl units for metabolic activities 

without the cost of ATP hydrolysis, this increased capacity may 

also represent a mechanism by which ALC can provide acetyl 

units in metabolically compromised situations. In insulindifferentiated 

3T3L1 cells, (-)-HCA was shown to inhibit 

lipogenesis and stimulate lipolysis (100). 

Incorporation of 3 H from 3 H 2 O was used to measure the rate 

of fatty acid synthesis in rat liver. In vivo inhibition of the rate 

of fatty acid synthesis in the rat liver was demonstrated after 

intraperitoneal/intravenous administration of (-)-HCA (101). 

The in vivo rate of lipogenesis was markedly decreased from 

[ 14 C]alanine following the administration of (-)-HCA either 

intraperitoneally or intravenously. Fatty acid and cholesterol 

syntheses were significantly inhibited by the oral administration 

of (-)-HCA only when the compound was given before the 

feeding period (65). The oral administration of (-)-HCA to rats 

significantly depressed the in vivo lipogenic rates in a dosedependent 

manner in the liver, adipose tissue, and small intestine 

and caused significant reductions in body-weight gain, food 

consumption, and total body lipid (66, 67). (-)-Hydroxycitric 

acid and (+)-allo-hydroxycitric acid were also investigated (102) 

for their effects on in vivo lipid synthesis under conditions of 

either high-carbohydrate feeding or 24 h fasting, and it was 

found that in fed rat, (-)-HCA significantly reduced the 

incorporation of labeled H 2 O and alanine into fatty acids and 

cholesterol. An increased rate of incorporation of labeled H 2 O 

into fatty acids but no change in cholesterol synthesis in the 

fasted rate suggested that (-)-HCA might be an activator of 

acetyl-CoA carboxylase. (+)-allo-Hydroxycitric acid was ineffective 

in modulating the rates of fatty acid synthesis under either 

nutritional condition. Both (-)-hydroxycitric acid and (+)-allohydroxycitric 

acid were shown to be in vitro activators of acetyl- 

CoA carboxylase, the former being a stronger activator. Thus, 

stereospecificity of the hydroxycitrate isomers was demonstrated 

in both the inhibition and stimulation of fatty acid synthesis 

possibly occurring at the level of acetyl-CoA carboxylase. 

Because the increase of citrate level could have allosterically 

activated acetyl-CoA carboxylase (103), this activation of acetyl- 

CoA carboxylase may be due to the increased level of citrate 

caused by the inhibition of citrate cleavage enzyme with (-)- 

HCA. 

In mature rat, the gold thioglucose-induced obese mouse, and 

the ventromedial hypothalamic lesioned obese rat, food intake, 

body-weight gain, and depression of body lipid levels were


reduced significantly by the chronic administration of (-)-HCA 

(104). Chee et al. (105) have observed species-specific response 

to (-)-HCA. Acute administration of (-)-HCA caused the 

depression of in vivo rates of fatty acid synthesis in the livers 

of chickens and rats. Chickens appeared to be more sensitive 

to the inhibitory effects of (-)-HCA than did the rats. Oral 

administration of (-)-HCA significantly reduced the rate of in 

vivo hepatic fatty acids and cholesterol synthesis, and there was 

a reduction in serum triglyceride and cholesterol levels in 

normolipidemic rats. It was also observed that (-)-HCA 

significantly reduced the hypertriglyceridemia and hyperlipogenesis 

in genetically obese Zucker rats, fructose-treated rats 

with elevated triglyceride, and Triton-treated rats (92, 106). 

Young Zucker lean (Fa/-) and obese (fa/fa) female rats were 

fed with (-)-HCA, and decreases in body weight, food intake, 

percent of body fat, and fat cell size in the lean rats were 

observed (107). In the obese rats food intake and body weight 

were reduced, but the percent of body fat remained unchanged 

and maintained a fat cell size equivalent to that of their obese 

controls. This study indicates that the obese rats, despite a 

substantial reduction in body weight produced by (-)-HCA, 

still defend their obese body composition. Rao and Sakariah 

(108) observed that inclusion of (-)-HCA in the lipogenic diet 

resulted in significant reduction in food intake, body weight, 

epididymal fat, and serum triglyceride in the albino rats and 

also a decrease in the feed efficiency ratio. The decreases in 

food intake, body-weight gain, and feed efficiency ratio brought 

about by (-)-HCA were dependent on the content of this 

compound in the diet. The study encouraged exploration of the 

efficacy of (-)-HCA in the control of obesity and hypertriglyceridemia. 

Effect of ())-HCA on Ketogenesis. Brunengraber et al. (95) 

reported that ketogenesis by livers of fed rats perfused without 

free fatty acid is strongly inhibited by (-)-HCA. It seems that 

such ketogenesis occurs via an extramitochondrial pathway that 

depends on the citrate cleavage reaction for its supply of 

extramitochondrial acetyl-CoA, which operates in carbohydratefed 

animals (109). However, the same parameter was not 

inhibited by (-)-HCA when livers from starved rats were 

perfused with oleate. On the other hand, the ketogenesis 

increased somewhat by (-)-HCA when livers from fed rats were 

perfused with oleate. The intramitochondrial pathway predominates 

either in starved animals or when the concentration of 

fatty acid is high or both. In the case of the rumen epithelium 

of sheep, the absence of any significant cytoplasmic component 

was emphasized by (-)-HCA, which should inhibit ketogenesis 

if ATP:citrate lyase plays any function in the process (110), 

but there was no such inhibition, lending support to the theory 

that ketogenesis proceeds exclusively through the mitochondrial 

pathway. 

Other Biological Effects of ())-HCA. (-)-HCA did not 

affect the rate of oxygen consumption by rat brain synaptosomes, 

and the activities of fatty acid synthase, carnitine acetyltransferase, 

glucose 6-phosphate-dehydrogenase, and acetyl-CoA 

synthetase but inhibited the activities of isocitrate dehydrogenase, 

malate dehydrogenase (decarboxylating), and aconitate 

hydratase at millimolar concentrations (50). (-)-HCA blocked 

dexamethasone stimulation of cytidylyltransferase but not of 

fatty acid synthase in lung tissue (111). 

Brunengraber et al. (95) observed that in rat liver, the 

inhibition of fatty acid synthesis by (-)-HCA was associated 

with an increase in the tissue content of glucose 6-phosphate 

and fructose 6-phosphate and a diminution in glycolytic 

intermediates from fructosebisphosphate to phosphoenol pyruvate. 

Presumably, the citrate content is elevated in cytoplasm 

in the presence of (-)-HCA. This can be expected to result in 

a reduced activity of phosphofructokinase because citrate is wellknown 

to act as an inhibitor of this enzyme (112-114). It has 

also been seen that AMP contents drop in the presence of (-)- 

HCA. This can also be expected to reduce the activity of 

phosphofructokinase, because AMP is an activator of this 

enzyme (115). The inhibition of phosphofructokinase by (-)- 

HCA in rat hepatocytes has also been reported by McCune et 

al. (116). It can be concluded that in rat liver, the inhibition of 

phosphofructokinase by (-)-HCA leads to the accumulation of 

glucose 6-phosphate and fructose 6-phosphate and the decrease 

of glycolytic intermediates beyond fructosebisphosphate as the 

reaction catalyzed by phosphofructokinase in glycolysis is 

irreversible and controls the glycolysis. 

Chronic metabolic acidosis increases proximal tubular citrate 

uptake, causing hypocitraturia associated with an increase in 

cortical ATP:citrate lyase activity and protein abundance. 

Hypokalemia, which causes only intracellular acidosis, also 

caused hypocitraturia and increased renal cortical ATP:citrate 

lyase activity. Inhibition of this enzyme with (-)-HCA significantly 

abated hypocitraturia and increased urinary citrate excretion 

in chronic metabolic acidosis and in K + depletion (117). 

These results suggest an important role of ATP:citrate lyase in 

proximal tubular citrate metabolism. (-)-HCA has been reported 

to alter the pyruvate metabolism by tumorigenic cells (118). 

Pyruvate consumption by tumor cells declined, but the mean 

percentage of oxidation increased with (-)-HCA. 

Possible Mode of Action on Reduction in Food Intake. 

The chronic oral administration of (-)-HCA to growing rats 

caused a reduction in body-weight gain, food consumption, and 

total body lipids. However, administration of equimolar amounts 

of citrate did not alter weight gain, appetite, or body lipids, and 

there was no increase in liver size or liver lipid content with 

either treatment. Paired feeding studies demonstrated that the 

reduction in food intake accounted for the decrease in weight 

gain and body lipid observed with (-)-HCA treatment, and this 

decrease in calorie intake was not responsible for the druginduced 

depression of hepatic lipogenesis (66, 67). Rao and 

Sakariah (108), in their studies, suggested that the reduction in 

appetite in (-)-HCA-fed rats seems to be a specific effect of 

(-)-HCA ingestion and not due to alterations of taste as the 

diet fed to control group contained citrate at a level equivalent 

to that of (-)-HCA in the experimental diet. In view of the 

close structural relationship of (-)-HCA to citrate, it is 

reasonable to believe that (-)-HCA does not affect the taste of 

the food. Panksepp et al. (119) evaluated the capacity of various 

salts of (-)-HCA to produce conditioned rejection of a 0.25% 

saccharin solution and concluded that the food intake was 

reduced by (-)-HCA only during the first hour following 

administration of the drug and the magnitude of appetite 

rejection did not correspond to the degree of conditioned 

rejection, lending support to the conclusion that the food intake 

reduction was not merely a consequence of aversive effects of 

the drug. 

A number of complex factors have been implicated in the 

appetite regulation and feeding behavior (67). Glucose utilization 

rates (120), unidentified humoral factor(s) in blood from satiated 

rats (121), enterogastrone (122) and other gastrointestinal 

hormones, plasma and brain tryptophan, brain serotonin interrelationships 

(123-127), and brain catecholamines (128) have 

all been suggested to play their role in the regulation of feeding 

behavior. Because (-)-HCA was demonstrated to inhibit fatty 

acid and cholesterol synthesis, presumably through a reduction


in acetyl-CoA pool in lipogenic tissues (65), the same effect 

would be expected in any cell possessing ATP:citrate lyase. 

Ricny and Tucek (129) have observed that the availability of 

acetyl-CoA had a decisive influence on both the rate of synthesis 

of acetylcholine and its steady-state concentration with glucose 

as the metabolic substrate in rat brain slices. Acetylcholine 

released by the phrenic nerve was measured in the isolated 

perfused rat hemidiaphragm; when (-)-HCA was added to the 

perfusate, the release of acetylcholine was stabilized at a level 

40% below the control value (130). (-)-HCA was reported to 

inhibit the synthesis of acetylcholine in rat brain slices (90, 131, 

132). These results suggested that citrate transport and subsequent 

cleavage give rise to acetyl-CoA as the principal precursor 

of acetylcholine synthesis. Sterling et al. (133) reported that in 

rat brain cortex, (-)-HCA reduced the incorporation of [ 3 H]- 

glucose and [ 14 C]-β-hydroxybutyrate to the acetyl moiety of 

acetylcholine. They suggested that in adult rats, β-hydroxybutyrate 

could contribute to the acetyl moiety of acetylcholine, 

possibly via the citrate cleavage pathway. Ricny and Tucek (134) 

observed the effects of (-)-HCA on the concentration of acetyl- 

CoA and acetylcholine in the tissue and on the release of 

acetylcholine into the media were investigated in experiments 

on slices of rat caudate nuclei incubated in different media. With 

glucose as the main metabolic substrate, (-)-HCA diminished 

the concentration of acetyl-CoA in all of the media used. ATP: 

citrate lyase appears to provide about one-third of acetyl-CoA 

used for the synthesis of acetylcholine. Gibson and Peterson 

(135) have shown that the (-)-HCA-reduced incorporation of 

[U- 14 C]glucose into acetylcholine was greater in septal than in 

hippocampal slices, indicating that acetylcholine metabolism 

varies regionally. Recently, Szutowicz et al. (136) reported that 

in Ca 2+ -activated rat synaptosomes, both synaptosomic acetyl- 

CoA and acetylcholine syntheses were suppressed by 27 and 

29%, respectively, by 1 mM (-)-HCA. The impairment of 

acetylcholine synthesis with (-)-HCA was also reported in the 

brain stem of neonatal rat (137). All of these in vitro studies 

revealed that (-)-HCA can depress acetylcholine synthesis in 

nerve tissues, although so far there is no evidence of reduced 

synthesis of acetylcholine in intact animals with the administration 

of (-)-HCA. Sullivan et al. (67) suggested that if (-)- 

HCA could penetrate the blood-brain barrier, then the depression 

of acetylcholine levels or rate of turnover in the brain 

resulting from a decreased precursor pool could affect cholinergic 

receptor systems that might be involved in feeding 

behavior. 

Fatty acid synthesis regulates fatty acid oxidation by a wellcharacterized 

mechanism (138, 139). In this paradigm, malonyl- 

CoA levels rise during fatty acid synthesis and result in 

inhibition of carnitine palmitoyl transferase 1 (CPT 1) mediated 

uptake of fatty acids into the mitochondria. This results in 

elevation of cytoplasmic long-chain fatty acyl (LCFA)-CoAs 

and diacylglycerol molecules that may play a role in signaling, 

which leads to the proposal that malonyl-CoA levels act as a 

signal of the availability of physiological fuels (140). One such 

proposal for maolnyl-CoA is the mediation of nutrient-stimulated 

secretion in the beta cells. Glucose-sensing neurons, which 

regulate feeding in the hypothalamus, share many features with 

the beta cells, including expression of glucokinase and the 

adenosine-sensitive potassium channel (141). The studies of 

Chen et al. (142) showed that (-)-HCA profoundly inhibited 

the glucose-stimulated insulin secretion (GSIS) from beta cells 

and also provided evidence for the pivotal role of malonyl-CoA 

suppression of CPT 1 with attending elevation of the cytosolic 

LCFA-CoA concentration in GSIS from the normal pancreatic 

beta cell. Moreover, Saha et al. (103) reported that inhibition 

of ATP:citrate lyase by (-)-HCA markedly diminished the 

malonyl-CoA level, indicating that citrate was the major 

substrate for the malonyl-CoA precursor, that is, cytosolic acetyl- 

CoA, and also there is sufficient evidence that (-)-HCA inhibits 

ATP:citrate lyase (47-51), limiting the pool of cytosolic acetyl- 

CoA, the precursor of malonyl-CoA. This type of regulation of 

malonyl-CoA level may affect the signaling of fuel status in 

hypothalamic neurons regulating feeding behavior, lending 

support that (-)-HCA may represent a biochemical target for 

the control of appetite/feeding behavior and body weight. Thus, 

(-)-HCA seems to act at the metabolic level and not directly 

at the central nervous system as classical appetite depressants 

do. 

())-HCA May Promote Glycogenesis, Gluconeogenesis, 

and Lipid Oxidation. The inhibition of ATP:citrate lyase by 

(-)-HCA causes less dietary carbohydrate to be utilized for the 

synthesis of fatty acids, resulting in more glycogen storage in 

the liver and muscles. Sullivan et al. (143) reported an increase 

in the rate of in vivo hepatic glycogen synthesis with the 

administration of (-)-HCA. Sullivan et al. (144) and Sullivan 

and Green (145) proposed that (-)-HCA acted primarily through 

its effects on the appetite, possibly involving increases in 

glycogen levels. Even though the administration of (-)-HCA 

increased the hepatic glycogen contents in rats, Hellerstein and 

Xie (146) demonstrated that neither hepatic glycogen nor the 

hexosephosphates are involved in the food-intake suppressive 

effects of (-)-HCA. It seems the increased hepatic fatty acid 

oxidation leading to increased levels of acetyl-CoA and ATP 

plays some role in this effect. 

In a well-fed state, the hepatic carnitine levels are far too 

low to activate CPT 1. The rate-limiting enzyme for hepatic 

lipid oxidation, CPT 1, is activated by exogenous carnitine and 

inhibited by malonyl-CoA. The lipogenesis inhibitor (-)-HCA 

can decrease the production of malonyl-CoA in hepatocytes by 

potent inhibition of ATP:citrate lyase and may activate CPT 1, 

which can facilitate lipid oxidation. Earlier studies demonstrated 

that (-)-HCA can reduce body-weight and fat accumulation in 

growing rats, owing to the reduction in appetite. From the above 

views McCarty (147) hypothesized that joint administration of 

(-)-HCA and carnitine should therefore promote hepatic lipid 

oxidation, gluconeogenesis, and satiety. In a recent study, joint 

administration of pyruvate, (-)-HCA, and carnitine to obese 

subjects was associated with a remarkable rate of body-fat loss 

and thermogenesis, strongly suggestive of uncoupled fatty acid 

oxidation (148). The reduction of free fatty acids by stimulating 

hepatic oxidation with (-)-HCA and carnitine may ameliorate 

risk factors associated with abdominal obesity (149). 

Sustained aerobic exercise requires a severalfold increase in 

hepatic glucose output. An increasing proportion of this elevated 

glucose output must be provided by gluconeogenesis. Thus, 

preadministration of (-)-HCA may aid endurance during 

postabsorptive aerobic exercise by promoting gluconeogenesis. 

Carnitine and bioactive chromium may potentiate this benefit. 

The utility of this technique may be greatest in exercise regimens 

designed to promote weight loss (150). The ability of exercise 

to selectively promote fat oxidation should be optimized if 

exercise is done postabsorptively (preferably during morning 

fasting metabolism), if (-)-HCA and carnitine are administered 

prior to exercise, if the exercise regimen is of moderate intensity 

and prolonged duration, and if no calories are ingested for 

several hours following exercise (151). 

Kriketos et al. (152) did not detect any effect of (-)-HCA 

administration on lipid oxidation, respiratory quotient (RQ), and


energy expenditure in humans during either exercise or moderately 

intense exercise. However, Ishihara et al. (153) demonstrated 

that chronic administration of (-)-HCA to mice 

lowered the RQ and increased lipid oxidation during both resting 

and exercising conditions and increased the endurance in 

exercise. These results indicated that the enhancement of 

endurance exercise by chronically administered (-)-HCA in 

mice might have occurred by the attenuation of glycogen 

consumption caused by the promotion of lipid oxidation during 

exercise. 

(-)-HCA AS A WEIGHT-CONTROLLING AGENT 

Weight gain occurs when the limited capacity for storing 

glycogen in the liver and muscles is attained, and beyond this 

point excess glucose is converted into fat and stored in fat cells 

throughout the body. (-)-HCA exerts its antiobesity effect by 

inhibiting ATP:citrate lyase, consequently inhibiting the cleavage 

of citrate to oxaloacetate and acetyl-CoA, a key molecule, which 

plays a critical role in energy storage as fat. Now, instead of 

wasting energy to synthesize fat, the energy is diverted to the 

production of glycogen in the liver and muscles. This slows 

the production of fatty acids, cholesterol, and triglycerides with 

the net effect of reduced fat production and storage (154). 

Preliminary research based on laboratory and animal experiments 

suggests that (-)-HCA may be a useful weight loss aid 

(101, 102). (-)-HCA has been demonstrated in the laboratory 

to reduce the conversion of carbohydrates into stored fat by 

inhibiting certain enzyme processes (49, 65). Animal research 

also indicated that (-)-HCA suppresses appetite and food intake 

to induce weight loss (66, 67, 104, 107, 108). 

Heymsfield et al. (155) stated in their publication that 

although (-)-HCA appears to be a promising experimental 

weight control agent, studies in humans are limited (156-160) 

and results have been contradictory. Supporting evidence of 

human (-)-HCA efficacy for weight control is based largely 

on studies with small sample sizes (157, 158), studies that failed 

to include a placebo-treated group (156), and use of inaccurate 

measures of body lipid change (158). Even though the effectiveness 

of (-)-HCA is unclear, at least 14 separate (-)-HCAcontaining 

products are sold over-the-counter to consumers 

(161). To overcome limitations of the above studies and examine 

the effectiveness of (-)-HCA for weight loss and fat mass 

reduction, Heymsfield and his colleagues at Obesity Research 

Center, University College of Physicians and Surgeons, New 

York, designed their investigation with rigorous controlled trials. 

Subjects were randomized to receive either active herbal 

compound [1500 mg of (-)-HCA per day] or placebo. Both 

groups were prescribed a high-fiber, low-energy diet, and the 

treatment period was 12 weeks. Body weight was evaluated 

every week, and fat mass was measured at weeks 0 and 12. On 

the basis of the results obtained from these experiments, 

Heymsfield et al. (155) concluded that a prospective doubleblind 

study failed to detect either weight loss or fat-mobilizing 

effects of (-)-HCA beyond those of a placebo. 

Rebuttal letters from Vladimir Badmaev et al. of Sabinsa 

Corp. (a manufacturer of standardized G. cambogia extract); 

James L. Schaller, Birchrrunville, PA; and Fabio Firenzuoli and 

Luigi Gori, St. Joseph Hospital, Empoli, Italy, published in the 

July 21, 1999, issue of the Journal of the American Medical 

Association were critical of Heymsfield’s studies. The letters 

are summarized below: 

• The results are contradictory to the positive results reported 

in several (-)-HCA clinical studies (156-160, 162), and it 

cannot be concluded from this single study that (-)-HCA is 

ineffective. 

• Previous studies and their own preclinical research (163) 

suggest that for (-)-HCA to effectively inhibit fat formation 

and body-weight gain, it needs to be administered with a simple 

carbohydrate-rich (lipogenic) diet. 

• The co-administration of (-)-HCA with a high-fiber diet 

may have inhibited the gastrointestinal absorption of (-)-HCA. 

This issue becomes critical with (-)-HCA; its reported efficacy 

in inhibiting intracellular enzyme ATP:citrate lyase depends 

entirely on the presence of (-)-HCA inside the target cell. The 

significance of (-)-HCA availability in the cytosol of the target 

cell for inhibiting lipid synthesis or ATP citrate lyase was 

confirmed (164). 

• The low-energy diet used in the study by Heymsfield et al. 

negated the utility of (-)-HCA. The study of Heymsfield et al. 

failed to evaluate (-)-HCA’s ability to reduce food intake by 

virtue of its energy-restricted protocol. 

• The dose of (-)-HCA used in the study was low compared 

with that used in earlier animal studies (66, 67). 

• Excess calcium used to stabilize the (-)-HCA molecule, 

common among products, reduces solubility and hinders bioavailability. 

A soluble Garcinia powder and liquid extract 

containing a lactone from (-)-HCA was compared with a 

calcium-type Garcinia powder administered in food to rats, and 

the liquid extract was proven to be more effective (165). Because 

blood (-)-HCA levels were not measured in the study, it was 

not known whether bioavailability was ensured in the studies 

of Heymsfield et al. (155). 

SOME POSSIBLE CONCERNS ABOUT (-)-HCA 

Animal studies indicate that (-)-HCA is no more toxic than 

citric acid itself, which is present in many foods in addition to 

being a normal intracellular compound. Also, (-)-HCA is a 

component of a natural product, which has been used in Indian 

cuisine as well as for medicinal purposes (1). Clouatre and 

Rosenbaum (154) pointed out that (-)-HCA has extremely low 

levels of toxicity. For example, recent oral toxicity studies 

performed at Wil Research Laboratories in Ashland, OH, found 

that 5000 mg/kg of body weight of (-)-HCA resulted in no 

visible symptoms of toxicity or deaths in laboratory animals. 

This is roughly equivalent to 350 g or 233 times the dosage of 

1.5 g/day of (-)-HCA that might be consumed by an averagesized 

person. Because G. cambogia has a long history of usage 

as a flavoring agent, preservative, and herbal tonic and there 

are no reports of toxicity regarding traditional use of the 

Garcinia extract, it is highly unlikely that there may be any 

possible negative effect that may occur due to excess intake; 

the possibility of bowel intolerance can be easily reversed by 

simply reducing the dosage. However, this problem has not been 

reported in animal studies at the levels that were necessary to 

reduce appetite. However, despite its inherent safety, (-)-HCA, 

like any other diet product, is not recommended for certain 

groups of people. (-)-HCA has impacts on the body’s production 

of fatty acids and cholesterol; therefore, it may directly 

influence the production of sterols, thus restricting the production 

of steroid hormones. As pregnancy is a time of extreme 

sensitivity to steroid hormones, products containing (-)-HCA 

should not be recommended during pregnancy. Likewise, 

women who are breast-feeding should also avoid (-)-HCA. 

Although experience with fruit sources of (-)-HCA shows that 

they are not dangerous to young children, they are advised not 

to consume (-)-HCA in large amounts for extended periods. 

One concern is about the time of administration and dosage 

considerations of (-)-HCA for its efficacy. Sullivan et al. (65) 

demonstrated that the effects of (-)-HCA in animals depend


on the time of administration in relation to a meal, with (-)- 

HCA maximally effective when administered 30-60 min prior 

to feeding. Most of the clinical studies including that of 

Heymsfield et al. (155) administered (-)-HCA ∼30 min prior 

to meals, which is the lower end of the maximally effective 

range. However, the administration of (-)-HCA postabsorptively 

in the studies of Kriketos et al. (152) showed a trend 

toward a lower RQ during (-)-HCA phase, although it was 

not statistically significant. Even though this study did not 

support the hypothesis that (-)-HCA alters the short-term rate 

of fat oxidation, the data certainly do not rule out its possibility. 

Another related concern is that (-)-HCA provided in divided 

doses was found to be more effective than the same amount 

given as single dose (67). In weight-loss protocols human doses 

ranging between 750 and 1500 mg/day of (-)-HCA (156-160) 

are the extreme lower end of the in vivo dose response range 

established by Sullivan et al. (66). 

As discussed earlier, the administration of (-)-HCA increases 

the rate of gluconeogenesis and ketone bodies formation (166), 

which can be deleterious in subjects with type-2 diabetes. In 

this situation, we can consider the hypothesis of McCarty (167) 

that excessive exposure of tissues to fatty acids is likely to be 

the chief cause of the various dysfunctions that lead to sustained 

hyperglycemia in type-2 diabetes. Disinhibition of hepatic fatty 

acid oxidation and inhibition of fatty acid synthesis with (-)- 

HCA and carnitine, as suggested earlier (147), have considerable 

potential as a new weight-loss strategy, but diabetics run the 

risk of further enhancing excessive hepatic gluconeogenesis. 

McCarty (147) hypothesized that the clinical utility of metformin 

in diabetes is probably traceable to inhibition of gluconeogenesis, 

and its use as an adjunct to (-)-HCA/carnitine treatment 

of obesity in diabetics deserves evaluation, particularly as 

metformin therapy itself tends to reduce body weight. Furthermore, 

metformin therapy will not impede the activation of fatty 

acid oxidation by (-)-HCA/carnitine and is likely to potentiate 

the appetite-suppressant and thermogenic benefits of this 

strategy. Indeed, because metformin has been reported to lower 

body weight and improve cardiovascular risk factors in obese 

nondiabetics, a broader application of an (-)-HCA/carnitine/ 

metformin therapy for obesity can be contemplated. 

(-)-HCA may have deleterious effects on insulin sensitivity. 

Many researchers have suggested that malonyl-CoA has an 

important role in transmitting the insulin signal in the cells (140, 

168, 169). It is well-known that (-)-HCA prevents the production 

of acetyl-CoA and subsequently malonyl-CoA (103); 

therefore, preventing its production may impair insulin responsiveness 

in some (or all) tissues. Thus, (-)-HCA is likely to 

have some effect on insulin sensitivity that can lead to type-2 

diabetes, that is, NIDDM. 

A role of malonyl-CoA in glucose-stimulated insulin secretion 

(GSIS) has been defined and a rise in malonyl-CoA, which 

preceded the insulin secretion in clonal pancreatic beta cells, 

was evident after exposure to glucose (170). Sener and Malaisse 

(171) reported the failure of (-)-HCA in the range of 1.0-2.0 

mM to affect the GSIS in glucose-stimulated intact pancreatic 

islets of rat. However, Chen et al. (142) explored the emerging 

concept of Prentki et al. (172) that malonyl-CoA generation with 

concomitant suppression of mitochondrial CPT 1 represents an 

important component of GSIS by pancreatic beta cells and 

observed that (-)-HCA profoundly inhibited GSIS and also 

provided more direct evidence for a pivotal role of malonyl- 

CoA suppression of CPT 1 with attendant elevation of the 

cytosolic long-chain acyl-CoA concentration in GSIS from the 

normal pancreatic beta cell. There may be another advantage 

of (-)-HCA in that it inhibits GSIS, which helps to keep this 

fat-storing hormone in check. 

High blood sugar levels suppress the burning of fatty acids 

for the availability of energy. Within the past few years, 

researchers have shown that high blood sugar levels generate 

malonyl-CoA, which is an inhibitor of carnitine palmitoyl 

transferase (CPT 1) that controls the transfer of long-chain fatty 

acyl (LCFA)-CoA into the mitochondria where these are 

oxidized. An increase in malonyl-CoA also results in the 

elevation of acyl-CoA, which triggers the release of insulin (140, 

168, 169, 173-176). Saha et al. (103) observed that inhibition 

of ATP:citrate lyase with (-)-HCA markedly diminished the 

increase in malonyl-CoA in skeletal muscle, indicating that 

citrate was the major substrate for malonyl-CoA precursor and 

cytosolic acetyl-CoA. As CPT 1 is considered to be a ratelimiting 

factor in the burning of fatty acids (177), the trick of 

long-term permanent fat loss is to increase the activity of CPT 

1. (-)-HCA can be used to increase the activity of CPT 1 as 

does L-carnitine and glucagon. Because research has shown that 

the conversion of carbohydrates into fat is prevented by (-)- 

HCA, a more important function of this incredible nutrient is 

its ability to increase the CPT 1 activity by decreasing the pool 

of acetyl-CoA, thus reducing the level of malonyl-CoA and 

raising the activity of CPT 1. 

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Received for review June 8, 2001. Revised manuscript received 

September 25, 2001. Accepted September 26, 2001. 

JF010753K

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